Redploying most of 127/8 as unicast public

Fri Nov 19 16:33:40 UTC 2021

> On Nov 19, 2021, at 07:39 , Joe Maimon <jmaimon at jmaimon.com> wrote:
> 
> 
> 
> Owen DeLong wrote:
>> 
>>> On Nov 17, 2021, at 21:33 , Joe Maimon <jmaimon at jmaimon.com> wrote:
>>> 
>>> 
>>> And I think the basic contention is that the vast majority of 127/8 is not in use. Apples to oranges, indeed.
>> This contention is provably false for some definitions of “in use”.
> 
> Determining the extent of this would be part of serious consideration.
>> 
>> In what way would the LLA or ULA above be meaningfully different from 127/8 as deployed?
> 
> Because 127/8 is the exact same number on every system and it is routed the same way on every system and every system can choose to use it how it and it alone wishes to.

But the proposal seeks to change that nature of 127.0.0.0/8 to make it more like LLA/ULA, so…

> So this make it a deterministic prefix solely in control of the local system without any external context to ever be taken into consideration, by convention and standard.

At the moment, that’s already true. AIUI, the proposal being discussed seeks to convert 127.0.0.0/8 outside of 127.0.0.1 (or at least outside of 127.0.0.0/16) into
routable GUA.

> LLA and ULA and whatever random prefix you may wish to use for loopback, whether in IPv6 or even IPv4 have none of these qualities.

And if we implement the proposal at hand, which as near as I can tell you are supporting, that changes.

>>> Doesnt IPv6 deserve its own instead of squatting on IPv4?
>> I don’t see any “squatting on IPv4” here.
> 
> It means that the only deterministic loopback prefix in IPv6 larger than a single address is the one IPv6 inherited from IPv4.

Well… Worst case, it could use ::ffff:7f00:0000::/96

Whether you consider that “squatting on IPv4” or not is left as an exercise to the reader. I do not, though I can understand and
must admit that it is equally legitimate if someone else does.

>> Since, as you point out, use of the other addresses in 127.0.0.0/8 is not particularly widespread,
> 
> This is not my point, it is the contention of the draft standard and it is something I would hope is taken into serious consideration and researched properly/
> 
> My point is that to the extent this is true, the value of the space for other purposes could very well warrant re-purposing.

Having trouble following your desired outcome here. It seems as if you both want 127.0.0.0/8 to retain it’s unique properties
as deterministically loopback only and also want the benefits of repurposing it as GUA.

Have cake, Eat cake, please to pick only one.

>>  having a prefix
>> dedicated to that purpose globally vs. allowing each site that cares to choose their own doesn’t seem like the best
>> tradeoff.
>> 
>> Owen
>> 
> But this is how it is to be done in IPv6, so lets get some lack-of-feature parity going with IPv4.

I’m all for IPv6 having better implementations than IPv4 rather than mere feature parity.

IMHO, having additional loopbacks be assigned from either LLA or ULA space (or even GUA, really)
where that is needed is a superior choice vs. 127.0.0.0/8.

For one thing, the alternative addressing schemes (other than LLA) allow for routing of the
addresses off the box even though they are configured on loopback interfaces. There are
a number of situations where this can be a useful way to ensure that the addresses remain
usable regardless of the up/down state of connectivity on any particular non-loopback
interface on the box.

It’s one of the reasons, for example, that virtually every IBGP speaking router has a GUA
or ULA/1918 loopback address which is routed in the IGP and almost all IBGP sessions
are terminated on those loopback interfaces.

Owen